The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Early automatic transmissions were hydro-mechanical devices in which varying hydraulic pressure developed within the transmission was utilized to sequence a plurality devices that controlled rotating members which achieved two, three or four forward gear ratios or speeds.
As the complexity of these transmissions increased, primarily in response to the demand for more gear ratios, electronic-hydraulic controllers were utilized. These devices received a plurality of signals from various sensors both inside and outside the transmission and commanded gear ratio selection based not only upon the sensed operating conditions by also programs, algorithms and data stored within the controller.
While providing greatly improved operating flexibility, such electronic-hydraulic controllers are not without their drawbacks. First of all, such controllers are typically mounted within the transmission where they are subjected to vibration and relatively high temperatures. Second of all, electrical power, data from external sensors and all other control circuits necessarily pass through the transmission housing, typically in a multiple conductor connector assembly. Not only does this connector represent a significant cost, it also can be a source of electrical problems resulting from intermittent or failed connections.
Thirdly, automatic transmission actuators and solenoid valves are often characterized, that is, their input power versus output pressure and flow is determined and such individualized data is stored in the electronic-hydraulic controller. If a component of the controller fails, it is generally standard practice to replace the controller. Not only is this practice expensive but it also requires that all the actuator or solenoid valve characterization data be restored in the new controller. If the controller failure is partial, it may be possible to recover and transfer the characterization data. If the failure is complete or essentially so, it will be necessary for the replacement controller to relearn the various characterizations through a relatively time consuming process.
Thus it is apparent that improvements in the art of electronic-hydraulic transmission controllers which address these drawbacks would be desirable and the present invention is so directed.